Improvements in valve designs used in internal combustion engines to control various functions of the engine and to enhance engine performance have been ongoing for many years. The quest for an internal combustion engine having an optimum efficiency has also been on the minds of engine manufacturers over time. By making improvements on valve functionality and design, engine manufacturers are able to solve many problems experienced by their customers and remain competitive in the marketplace.
One aspect of engine performance that has received attention in recent years is exhaust gas recirculation, especially in a diesel engine. In a diesel engine, an excess amount of air is usually introduced into the combustion chamber. Therefore, exhaust gas recirculation operation for a diesel engine must be controlled relative to the excess. Since the amount of excess air decreases in accordance with the increase of engine load, it would be desirable to manufacture a valve device for controlling the amount of gas and air directed to the engine in such a way that the amount of recirculated exhaust gas introduced into the engine intake passageway is decreased while the amount of intake air directed to the engine is increased in accordance with an increasing engine load. In order to effectively control exhaust gas recirculation, the relationship between the load of the engine and the ratio of the amount of recirculated exhaust gas to the total mount of fluid directed to the engine should be determined.
Various types of valve designs exist which utilize geometrically shaped openings to control fluid flow for achieving desired engine operation characteristics. One reference which discloses such a design is U.S. Pat. No. 4,154,263 to Cary. This reference discloses a control valve having a movable valve element positioned in a cylindrical housing with triangularly shaped openings formed therein for variably controlling fluid flow depending on the relative position of the valve element. The apertures may take a variety of shapes to achieve the desired flow characteristics with respect to the stem travel. The valve design of Cary, however, includes apertures formed on the upstream side of the valve which decrease the effective controllability of fluid flow. In addition, the valve element of Cary comprises a spool valve structure which often does not provide an adequate seal along the slidable clearance between the valve element and housing. The spool valve structure of Cary also has many parts and is costly to manufacture which would make it undesirable for many applications.
Two references which disclose an improvement to the Cary design in terms of enhancing flow characteristics are U.S. Pat. Nos. 5,205,537 and 5,368,276, both to Pfeiffer. These references disclose a control valve structure including a control valve element and a flow orifice or port having a variable cross-section (i.e., a teardrop or egg-shaped cross section). Movement of the valve element varies the cross sectional flow area based on the shape of the flow port to provide enhanced area and flow range ability. The valve structures of Pfeiffer, however, are spool valve designs which are costly to manufacture and may not provide adequate sealing in high pressure environments. In addition, the flow port is formed in the valve element instead of the valve body which also increases manufacture and repair costs. Furthermore, the Pfeiffer valve is designed to control the flow of particulate solids and not gaseous fluids generated by an internal combustion engine.
U.S. Pat. No. 4,237,837 to Toda et al. discloses an exhaust gas recirculation control valve for a diesel engine that is designed to achieve a low rate of increase in the flow area of the exhaust gas when the valve is opened from its fully closed position. Toda et al. discloses a complex valve design comprising many parts for merely actuating the valve element. In addition, the valve of Toda et al. does not provide a downstream outlet port formed in a valve cavity which is desirable for effective control of flow characteristics.
It is evident, based on the art discussed above, that the manufacturing industry has yet to develop a simple, inexpensive and compact valve with improved flow control characteristics for effectively controlling the flow of fluid therethrough.